In the art of beds, the most common form of bed comprises an elongate, flat, horizontal, rectangular body supporting mattress of soft, resilient and/or yielding material and an elongate floor engaging bed frame arranged beneath and supporting the mattress above the floor. Such beds have forward head ends and rear foot ends.
One special class of bed, which is widely used in hospitals and the like, includes an articulated mattress supporting frame which is such that it can be operated to elevate the head end of the mattress whereby the head end portion of the mattress is longitudinally and upwardly inclined relative to the remainder of the mattress and so that a person lying or engaged on the mattress is comfortably supported in a semi- or substantially upright sitting position. The ordinary articulated bed of the character referred to above is commonly constructed and operable to elevate and bend or break that portion of its related mattress occurring at and beneath the knees of a person lying on the bed to comfortably elevate and support the legs of that person in an elevated bent condition, when desired.
In the ordinary articulated bed frame, the normally horizontal, rectangular, mattress supporting frame is a sectional structure comprising a head end section, a foot end section and a central or intermediate section. The several sections have laterally extending or transverse forward and rear end edges. The rear edge of the head section and the forward edge of the central section are pivotally connected together on a fixed horizontal axis extending transverse the frame, while the rear edge of the central section and the forward edge of the foot end section are pivotally coupled together on a vertically and longitudinally shiftable transverse axis. The rear edge of the foot end section is free to shift longitudinally and is, in some instances, shiftable vertically.
The ordinary articulated bed frame structure of the character referred to above also includes manually operable or motor driven jack mechanisms related to the head sections of the frames to pivot the forward edges of those sections of the frames up and down. Second and similar jack mechanisms are provided to raise and lower the pivotally connected edges of the central and foot end sections and, if necessary, third similar jack mechanisms can be provided to raise and lower the rear edges of the foot end sections.
In the case of ordinary fiber or plastic foam filled fabric covered mattresses used in combination with articulated bed frames of the character referred to above, the mattresses substantially freely break or bend transversely along lines parallel with the axes between the adjacent sections of the frames to establish the desired mattress configurations.
Further, in the art of bedding, flotation mattresses comprising water filled bladders of supple and flexible sheet plastic have become quite common in recent years and are now recognized as affording support for the human body which is notably superior to that support which is afforded by common fiber or foam plastic filled fabric covered mattresses.
The superior body support afforded by flotation mattresses is such that the use of such mattresses is being recommended and/or required by an ever-increasing number of experts in the fields of medicine and physical therapy.
As a result of the above, in the recent past, efforts have been made to support water-filled plastic bladder-type flotation mattresses on articulated bed frame structures of the character referred to in the preceding and to thereby attain the benefits afforded by flotation mattresses in combination with the benefits afforded by articulated bed frames. Such efforts have met with little or no success.
The lack of successful use of flotation mattresses in combination with articulated bed frames of the character referred to above resides in the fact that ordinary flotation mattresses comprise bladders of soft, supple and flexible sheet plastic with vertically spaced normally parallel horizontal, top and bottom walls and vertical side and end walls about and between the top and bottom walls. The two horizontal walls are established of two sheets of plastic sheet stock and the side and end walls are normally established by vertically downwardly and upwardly turned and suitably cut marginal extensions on the top and bottom walls, which extensions have related edges arranged in lapped engagement with each other and are sealingly fixed together by continuous lines of thermal welding. Accordingly, the side and end walls of such mattresses are characteristically interrupted and divided by welded seams. In addition to the above noted seams, the four vertical corner edges of such mattresses are often established by welded seams.
When thermally welding the seams in the sheet plastic of mattresses of the character referred to above, heat and pressure is applied on and between the plastic sheeting to be welded along weld lines. The applied heat and pressure stretches, draws and causes the plastic material to flow and weld together. The stretching, drawing and/or flowing of the material results in notably reducing the wall thickness of the sheet plastic material adjacent the weld lines and materially weakens the resulting bladder structures adjacent the weld lines.
The above noted weakened areas of the bladders are subject to rupturing and tearing when excessive internal pressures, in the bladders, are encountered.
In addition to the above, thermal welding also tends to cause hardening or embrittlement of the welded material to further weaken the resulting structures.
When water filled flotation mattresses of the character referred to above arre related to articulated bed frames and are caused to be bent or broken along one or more transverse lines by operation of the bed frames, the bending or breaking of the mattresses, in effect, squeezes or pinches off portions of the mattresses, displacing the water adjacent thereto and materially increasing the hydraulic or fluid pressure within the mattresses. In the case of ordinary floation mattresses of the character referred to above, the increased pressures generated within the mattress upon bending or breaking them, as noted above, is sufficient to cause the weakened portions of the mattress structures adjacent the weld lines to rupture or burst. The above rupturing or bursting of such mattresses occurs in spite of the fact that the portions of the mattress which are not weakened by welding or the like are theoretically of sufficient strength to withstand the noted increased pressures.
Attempts to overcome the above noted weaknesses in ordinary flotation mattresses by increasing the wall thickness of the sheet material employed to establish the mattresses and thereby provide a greater amount of material and resulting greater strength at the weld lines, has resulted in mattresses which are not sufficiently supple and flexible, or which are too hard and stiff to afford the sought after and desired body support.
Another shortcoming found in the use of conventional flotation mattresses in combination with articulated bed frames of the character referred to above resides in the fact that when the bed frames are operated to bend or break the mattresses, the unrestricted flow or displacement of the single and large volume of water throughout the planes of the mattresses results in situations where insufficient water is let to remain beneath some portions of the bodies of persons engaged on the mattresses to prevent their bodies from causing the top walls of the mattresses to engage and stop or "bottom out" on the bottom walls thereof; and moves or displaces excessive volumes of water beneath other portions of the bodies of the persons to elevate those portions of their bodies, whereby desired and sought after body support is unattainable.